Silencer



Dec. 9, 1941.

R. B. BOURNE SILENCER Filed Ma 18, 1940 K1 1 I [V 14 L1 INVENTOR fFozAAm B. flown/z BY y I Z ATTogNEYs Patented Dec. 9, 1941 UNITED STATES- PATENT OFFICE SILENCER Roland B. Bourne, West Hartford, Conn., assignor to The Maxim Silencer Company, Hartford, (loan, a corporation of Connecticut Application May 18, 1940, Serial No. 335,878

Claims.

the type described. The present application is a 10 continuation in part of said prior application, and contains matter divided therefrom.

Two species of silencers of this'general construction have been proposed. In each the silencer included one or more chambers, into which two open-ended pipes led from'opposite ends. In one of these species one of the pipes was provided with a series of holes or a continuous slot within the chamber, to permit lateral escape of the gas and sound waves, while the other pipe was imperforate. In the second species both of these pipes were provided with perforations or slots extending throughout that portion of the length of the pipe within the eass. sound waves is'concerned the first type is the more efllcient, but possessed a tendency to transmit sounds of frequencies which prove upon a measurement to be those of the fundamental and These harmonics of the imperforated' pipe. sounds are not, therefore, transmitted in the proper sense, but are created within the device itself as the imperforated pipe sounds off at its own natural frequency when its open end is struck by a gas pulse.

It is the object of the present invention to improve upon these prior devices by preserving the silencing power of devices having one imperforate tube'while avoiding thetendency to create .sound within the silencer itself." This hasdfl been done in the manner described in my prior application Serial No. 291,820 referred to above. In accordance with the principles set forth in that application the imperforate tube is provided with an auxiliary system coupled to the 4 interior of the tube at discrete points having a." predetermined relationship to the longitudinal dimensions of the tube, and having the acoustic conductivity of its coupling sufliciently small so that the addition of this auxiliary system causes 50 .a'casing ll divided into chambers II and I! by a partition II.- An inlet pipe It leads into the substantially no change in the natural resonating frequencies of the tube itself.

The auxiliary system may be composed of a conduit of the same length as the tube, either tubular or annular, closed at its ends, and coupled 56 As far as the attenuation of impressed 25 (Cl. ISL-54) to the tube at points spaced at distances from one end of the latter equal to L/2 and L/4, where L is the length of the tube. Alternatively the auxiliary system may be composed of the interior.

of the chamber itself coupled to the pipe through apertures spaced as in the first case. In either case the areas of the coupling apertures are kept low enough so that no appreciable change in the natural resonant frequencies of the pipe is caused. If the pipe is circular the diameter of the holes is preferably within 3% to 20% of the pipe di ameter. If the pipe is annular the diameter of the holes is kept between 3% to 20% of the quantity where S is the cross-sectional area of the annular gas passage. The spacing of the holes along the pipe is preferably kept close to the points mentioned, although a variation of a few percent will not cause standing waves to appear on shock excitation.

Having thus described the basic principles of the invention several specific forms of silencing apparatus in which the invention is used will now be described with reference'to the accompanying drawing, in which:

Fig. 1 is a longitudinal section through a silencer having two chambers Joined by a connecting pipe of annular form, and in which shock excitation of this pipe is prevented by a tube with closed ends coupled to the annular Fig. 2 is a section on line 2-2 of Fig. 1; Fig. 3 is a longitudinal section through a similar form of silencer in which the connecting pipe is tubular and the auxiliary system is formed by an annular passage with closed ends;

Fig. 4 is a section-on line 0-4 of P18. 3;

Fig. 5 is a longitudinal section throifih another form of silencer in-whlch the inlet and exhaust conduits have closed ends with lateral escape openings formed by one ormore tapering slots and in which the auxiliary system is formed by the'lnteriors of the silencing chambers;

Fig. 6 isasectiononllne Hofl'lgj;

Fig.1 is a further modification illustrating the use .of a plurality ofoonnecting tubs; and Fig. 8 is a section onllne H ofFig. 'I.

The silencer shown in Figs. 1 and 2 comprises chamber i I and an outlet pipe ll leads out of the chamber l2. The inlet and exhaust pipes have lateral escape openings ll shown in the form 2 of a slot at the left in Fig. 1 but which may be composed of a number of perforations if desired,

as shown at H3 at the right in Fig. 1. The perforations or slot preferably extends substantially throughout that portion of the pipe within the chamber. An open ended tube ll' extends between the two chambers H and I2, passing through the partition l3 supported within this tube as by clips i8 is a relatively small tube [9 havingits ends closed at 20 and having perforations 2| and 22 positioned respectively at the half and quarter point. As will be seen the gas passage within the tube I1 is annular, comprising the space between the walls of the tubes l1 and I9 and this annular space is coupled to the closed resonating tube 20 through the holes 2| and 22.

The silencer shown in Figs. 3 and 4 is generally similar, and the chambers and the inlet and outlet pipes have therefore been indicated by the same reference characters. The connecting pipe, however, is formed by a tubular conduit 25 open at its ends and surrounded by a second pipe 26. The space between the two pipes is closed off by annular partitions 21 at each end.

' A series of holes in the pipe 25 are formed at 28, 29, 30, and 3|, these being positioned at distances L/2, 3L/8, L/i, and L/8 respectively. This is the preferred spacing of the coupling apertures but if desired one or both of the openings 29 and Si may be omitted in case the harmonics suppressed by these openings are not naturally strong enough to be of consequence.

The silencer shown in Figs. and 6 is of still different construction.- The casing 35 is divided by a transverse partition 36 into two chambers 31 and 98. Inlet and exhaust pipes 39 and iii enter from opposite ends of the casing and in this case may if desired be secured as by welding to the partition 31 which thus acts to close off the ends of the tube. Each tube is provided with a slot ll extending substantially throughoia, that portion of the pipe contained within the casing and tapering in a direction toward the central partition. The connecting tube 42 has its ends open and extends through the central partition 36 into adjacency with the ends, of the casing 35 there being, of course, a sumcient space to permit the free flow of gas into or out of the end of the tube. The tube has a series of holes 43 preferably positioned as in Fi 3.

The silencer shown in Figs. '7 and 8 has a casing 45 divided by a transverse partition 46 into throughout that portion of its length contained within th casing and the pipes terminate with open ends spaced from the central partition a distance to permit the free flow of gas.

A plurality of connecting tubes 52, generally two in number, pass through the central partition and terminate short of the ends 01 the casing. Each of these tubeshas a series of holes 53 opening out into the space within the casing. It will be observedthat certain of these holes enter one of the chambers and certain of them enter the other since the holes are in one half of the connecting tube and the partition 46 is not quite central. If the holes were all placed in the other half of the connecting tube they would all enter the larger chamber 41 and either form of structure may be used. It is generally preferable, however, to arrange the holes as shown since gas flow through these holes is not desired, particularly in the larger inlet chamber 41, since the silencing however,'the total area of the holes is sufliciently small so that they will not act as gas passages to an extent sufficient to make an appreciable difference in performance between the forms of Figs. 1 and 3 and those of Figs. 5 and 7. As the latter forms are somewhat cheaper in construction they will in general be preferable.

It will be understood that the forms of lateral escape opening in the inlet and outlet pipes may be varied as desired and that the particular form of escape opening shown in one figure may be replaced by that shown in another without making any marked change in the performance of the device. It will also be understood that in any of the cases a suflicient number of holes are used to prevent the setting up of such standing waves as would otherwise prove bothersome. In no case however will it generally be necessary or desirable to use more than the four holes shown as these are suiiicient to prevent all usual harmonics being set and a much greater number of holes merely converts the pipe into one of a shorter length in which standing waves systems may be set up. As has been previously stated, the area of the holes should be kept down sufficiently to prevent the system being converted to a compound one in which the connecting pipe and the auxiliary system resonate together at some frequency different from the natural frequency of the pipe itself.

I claim:

'1. A silencing device comprising a chamber, an open ended conduit entering said-chamber and having one or more lateral escape openings in its walls distributed throughout substantially the entire length ofthe conduit within the chamber, a second conduit having a portion extending into said chamber in a direction opposed to that of the first conduit, one of said conduits serving as an inlet and the other as an outlet, the second conduit having perforations in its walls localized at distances substantially equal to L/2, L/4 and nL/ 8 from one end of the conduit, where L is the length of the second conduit and n is 1 or 3, said perforations being of a diameter from 3% .to 20% of that of the conduit.

2. A silencing device comprising a chamber,'an open ended conduit entering said chamber and having one or more lateral escape openings in its walls distributed throughout substantially the entire length of the conduit within the chamber, a second conduit having a portion extending into said chamber in a direction opposed to that of extending the entire length of the second conduit into which said perforations open.

3. A silencing device comprising achamber, an

open ended conduit entering said chamber, extending substantially throughout the length thereof, and having one or more lateral escape openings in its walls distributed throughout substantially the entire length of the conduit within the chamber, a second conduit having, a portion extending into said chamber in a direction opposed to that of the first conduit and being laterally offset from the first conduit during a substantial portion of its length, one of said conduits serving as an inlet and the other as an outlet, the second conduit having perforations in its walls localized at distances substantially equal to L/2, L/4, and nL/8 from one nd of the conduit, where L is the length of the second conduit and n is l or 3, said perforations being of a diameter from 3% to 20% of that of the conduit.

4. A silencing device comprising a chamber, an open ended conduit entering said chamber, extending substantially throughout the length thereof, and having one or more lateral escape openings in its walls, distributed throughout substantially the entire length of the conduit within the chamber, a second conduit having a portion extending into said chamber in a direction opposed to that of the first conduit and being laterally offset from the first conduit during a substantial portion of its length, one of said conduits serving as an inlet and the other as an outlet, the second conduit having perforations in its walls localized at distances substantially equal to L/2, L/4, and nL/8 from one end of the conduit, where L is the length of the second conduit and n is 1 or 3, said perforations being of a diameter from 3% to 20% of that of the conduit, and a closed-ended casing extending the entire length of the second conduit into which said perforations open.

5. A silencing device having an enclosure through which gas may flow, and a conduit acoustically coupled at one end with said enclosure, said conduit having perforations in the wall thereof localized at distances substantially equal to L/2, L/4, and nL/8 from one end of said conduit, where L is the length of the second conduit and n is 1 or 3, at least some of said perforations opening into said enclosure.

6. In a muflier having two compartments and v an open-ended conduit connecting said compartments, an acoustic resonator acoustically coupled to said conduit at a point of maximum pressure change for a standing wave system therein, and tuned to resonate at the frequency of said system, the conductivity of said coupling having a value between 3% and 20% times \/4S/1r, where S is the cross-sectional area of the conduit.

7. A silencing device comprising a plurality of,

chambers, an open-ended inlet tube opening into one of the chambers, an open-ended exhaust tube opening into another of said chambers, and an open-ended tube connecting said chambers, the inlet and exhaust tubes each having one or more lateral escape openings in the wall thereof distributed substantially throughout the entire length of said conduit Within th chamber, said connecting tube having perforations in its walls localized at distances substantially equal to L/2 and L/4 where L is the length of the connecting conduit.

8. A silencing device comprising a plurality of chambers, an open-ended inlet tube opening into one of the chambers, an open-ended exhaust tube opening into another of said chambers, and an openended tube connecting said chambers and overlapping the inlet and exhaust tubes, the inlet and exhaust tubes each having one or more lateral escape openings in the wall thereof distributed substantially throughout the entire length of said conduit within the chamber, and

said connecting tube having'a plurality of perforations in its walls at distances localized substantially from one end of the tube taken from the series L/2, L/4, L/8, 315/8, and being restricted to a diameter between 3% and 20% of that of the connecting conduit.

9. A silencing device comprising a plurality of chambers, an open-ended inlet tube opening into one of the chambers, an open-ended exhaust tube opening into another of said chambers, and an open-ended tube connecting said chambers and overlapping the inlet and exhaust tubes, the inlet and exhaust tubes each having a slot in its wall extending throughout substantially the entire length of said conduit within the chamber, and said connecting tube having a plurality of perforations in its walls localized substantially at distances from one end of the tube taken from the series L/2, L/4, L/8, 3L/8, and being restricted to a diameter between 3% and 20% of that of the connecting conduit.

10. A silencing device comprising a plurality of chambers, an open-ended inlet tube opening into one of the chambers, an open-ended exhaust tube opening into another of said chambers, and an open-ended tube connecting said chambers and overlapping the inlet and exhaust tubes, the inlet and exhaust tubes each having a slot in its wall extending throughout substantially the entire length of said conduit within the chamber and tapering towards the open end of the conduit, and said connecting tube having a plurality of perforations in its walls localized substantially at distances from one end of the tube taken from series L/2, L/4, L/8, 3L/8 and being restricted to a diameter between 3% and'20% of that of the connecting conduit.

ROLAND B; BOURNE. 

